https://www.stereophile.com/content/anthem-electronics-str-da-integrated-amplifier-measurements
If the DAC in the STR preamp is similar to better to the one in the STR integrated, I highly doubt you will get an audible improvement regardless of DAC. If you use ARC, then you are digitizing the analog inputs anyway, so now the ADC and DAC are active, on top of the external DAC, so that’s a lot of THD, IMD, channel separation, etc. that gets compounded through each stage, not to mention the analog inputs themselves aren’t ultra clean. You may make the sound different, but I highly doubt you will make it cleaner; and if you wanted different, just mess with ARC.
If the DAC in the STR preamp is similar to better to the one in the STR integrated, I highly doubt you will get an audible improvement regardless of DAC. If you use ARC, then you are digitizing the analog inputs anyway, so now the ADC and DAC are active, on top of the external DAC, so that’s a lot of THD, IMD, channel separation, etc. that gets compounded through each stage, not to mention the analog inputs themselves aren’t ultra clean. You may make the sound different, but I highly doubt you will make it cleaner; and if you wanted different, just mess with ARC.